This invention relates to an IC (integrated circuit) card, and more particularly to an IC card which contains a rewritable semiconductor memory.
An IC card with data processing function has recently been put into practical use. This IC card contains a central processing unit (CPU) and a rewritable data memory, such as an electrically erasable programmable read only memory (EEPROM), or a random access memory (RAM) which is backed up by the battery. The data memory is connected to the CPU. The IC card has on its surface terminals for data transfer with the external device such as the terminal devices. The terminals are not necessary if data transfer is a non-contact type, for example, via a microwave or an optical beam. This type of IC card can be considered to be a microcomputer in the shape of a card. However, the major difference of this type of IC card from the ordinary microcomputer resides in that, because of its card-like shape, the CPU and the data memory of the IC card are physically limited. Therefore, the capacity of the data memory has also a limit. It follows that an efficient use of the memory is required.
Recently, the IC card used for multi-purposes, called a multi-use type IC card has been proposed. In the multi-use type IC, a plurality of files are stored in the data memory, and the file access and file control must be controlled effectively.
The data memory in an IC card has been used in the following two ways:
(1) The entire memory space is sequential. The memory addressing is based on the absolute address supplied from the external device.
(2) The memory is segmented into a plurality of blocks. The memory addressing is performed by the logical address, viz., the offset value from the top address of the block.
The way (1) of the IC card memory has the following drawbacks.
(a) The layout of the memory has to be determined in system design. When it is requested later to expand the file or to register a new file, it is difficult to satisfy such a request.
(b) The memory area for each file must have a larger area than the expected maximum file. It often entails unnecessary use of the memory.
(c) For defective addresses (memory cells), if present, the IC card cannot take any measure by itself.
(d) Addressing is complicated.
The way (2) also involves the above problems (a) to (c).